The project involves the study of the physiological organization of neurons of the visual system of primates. Studies were carried out to characterize: (1) the chromatic organization of the peripheral region of the "center-surround" organization of the receptive field of color-opponent ganglion cells, and (2) the degree of heterogeneity of properties among color-opponent ganglion cells whose receptive fields are located in the retinal periphery. During the period covered, analyses of some prior studies were completed, and results are being prepared for publication. (1) Comparison of the results of area-threshold measurements and of chromatic mapping of the receptive field with a small test spot showed that a fraction of the color-opponent ganglion cells of macaque retina has antagonistic center and surround responses mediated in part by the same type of cone mechanism. The apparent frequency of these cells increases towards the retinal periphery, and their resulting center-surround organization provides a simple and direct model for the development of the recently reported "modified Type II" neurons of the striate cortex of macaques. (2) Further studies of the degree of homogeneity of peripheral color-opponent ganglion cells are consistent with the existence of two main cell classes that differ in terms of conduction velocity, receptive-field center size, and degree of surround antagonism. Preliminary results suggest that some cells of one of these groups loose color-opponent properties in the far periphery, developing a chromatic organization similar to that of the color non-opponent, broad-band ganglion cells.